CODEWITHSUNDEEP
optimizationiteratorfortrando-loops
Jon
Jon

Reputation: 11

gfortran optimization causes fortran do-variable loop error during runtime

I have written a fortran routine that uses some legacy fortran 77 code for finite elements. However, with a particular mesh, when the -O optimization flag is turned on, an important do-loop iterator is somehow being modified, even though fortran supposedly prohibits this. I have compiled this code using gfortran4.5 with the -fcheck=do run-time checking enabled and it has verifies what I've noted above. A runtime error occurs, only when optimizations are turned on and points directly to the do-iterator.

Using gdb on optimized code seems (while it seems erratic - lines bouncing back and forth) seems to clearly indicate that the do-iterator somehow gets set back to zero, and essentially this causes a nice infinite loop.

Any suggestions as to how to hunt down and fix whatever is causing this bug would be greatly appreciated, as I'd like to make sure the whole project can be consistently compiled with the same flags.

Upvotes: 1

Views: 1160

Answers (1)

janneb
janneb

Reputation: 37248

You say that you use fcheck=do; why not go all the way and use fcheck=all? What you're seeing sounds like a typical case of memory corruption due to an array bounds violation, which fcheck=all can in some cases catch. Where the array bounds checking doesn't work that well is with implicit interfaces and incorrect bounds being passed; a solution here is to put your procedures into modules, allowing the compiler to check interfaces.

And, like Jonathan Dursi said, consider using a tool like valgrind.

Upvotes: 4

Related Questions